Fueling for Peak Marathon Performance

An Hour Into Training, Start Refueling Your Tank

The goal on longer training runs, as well as marathon race day, is to preserve glycogen and tap into the ever-so-abundant amount of fat stores within the body. Remember that "fats burn in a carbohydrate flame."

Picture carbohydrates as kindling under a fire and fat as a big log. Without an adequate amount of kindling or carbohydrate, the body fails to burn fat and starts to deplete precious muscle glycogen stores until the fuel tank is empty, leading to that ugly "wall" and mind-boggling "bonking" that generally occurs between mile 18 and 20 in a marathon (and even sooner if pre-race fueling is inadequate).

In order to prevent "the wall" and "bonking" and increase fat burning capabilities, it's essential to start refueling the body's fuel tank after about 60-90 minutes of moderate-to-high intensity exercise.

The following equation can be used to determine hourly calorie needs following 60-90 minutes of exercise: 2 calories x lean body weight in pounds

More: Perfectly Natural Fuel

High-glycemic carbohydrates (e.g., energy gels, sports drinks) should make up the majority of calories ingested during a marathon, but inclusion of smaller amounts of protein during a marathon may help enhance endurance performance by as much as 24 percent.

As a means to reap the potential benefits of protein, athletes engaged in prolonged training or racing (more than three hours) should aim at consuming up to 1/8 gram of protein per pound of lean body weight or approximately one gram of protein for every 4-7 grams of carbohydrate ingested.

Personally, I mix my customized formula into a concentrate or paste and place it into a Fuel Belt or gel flask with water. Beyond 60-90 minutes of racing, I'll take shots from my flask along with course-provided water every 15 minutes, which allows my fueling to occur at a steadier rate. It also helps prevent unwanted stomach issues that can arise when too many calories are ingested in a bolus dose.

This is my customized InfinIT Nutrition Formula (per 20-ounce serving): 192 calories, 42 grams carbohydrate, 6 grams protein, 480 mg sodium, 138 mg potassium, 60 mg magnesium. 30 mg calcium

More: Natural Race Food Alternatives

Drink Up!

The human body can last a lot longer without food than it can without water. In fact, dehydration (or loss of fluids) can have a profound effect on marathon performance. Runners who blow by the initial marathon water stops tend to be reeled in during the later stages of the race as the onset of "thirst" can trigger an approximate 15 percent decline in their performance capability.

Besides thirst, symptoms of dehydration include muscle cramping, muscle fatigue, nausea, vomiting, diarrhea and chills. In the most severe cases of dehydration, the body's core temperature may increase to 108 F, which if prolonged, will lead to kidney failure and death.

More: Hydration Basics

To avoid severe cases of dehydration, runners should aim to replace 0.5-1 liter of fluid each hour during runs, implementing an electrolyte-rich beverage (e.g. sports drink) after 60 minutes of running.

A sports drink should contain the following approximate concentration of electrolytes per 8-12 fluid ounce serving:

  • Sodium: 150-250 mg
  • Chloride: 45-75 mg
  • Potassium: 50-80 mg
  • Magnesium: 20-30 mg
  • Calcium: 10-15 mg

  • Those vulnerable to muscle cramping will also benefit from ingesting a sodium-rich food or beverage as part of their pre-race nutritional plan.

    More: 15 Hydration Facts for Athletes

    Active logo Perfect your nutrition to boost your performance. Sign up for a marathon race near you.
    • 2
    • of
    • 2

    About the Author

    Kim Mueller, M.S., R.D.

    Whether you're at the front, middle or back of the pack, you can find helpful training tips, injury prevention tips and the latest product reviews on Competitor.com.
    Whether you're at the front, middle or back of the pack, you can find helpful training tips, injury prevention tips and the latest product reviews on Competitor.com.

    Discuss This Article